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The potential controlling silver catalysis for Ru(bpy)32+electrochemiluminescence (ECL) signal at a special potential −0.4∼1.25 V was newly developed as the new ECL signal amplification strategy for ultrasensitive protein detection. Firstly, the wheat-like deposited silver (DpAg) particles were modified on the bare glass carbon electrode (GCE) surface by cyclic voltammetry deposition to capture the primary antibodies and then bind the antigen analytes. Secondly, as a sandwich immunoreaction format, the secondary antibodies conjugated with the Ru(bpy)32+-doped Pt (Pt@Ru) nanoparticles by the multi-sites biotin/streptavidin (SA) affinity can be captured onto the electrode surface to generate ECL signal. In the proposed Ru(bpy)32+ECL system without any co-reactant, the detected ECL signal was amplified due to following multiple amplification strategies: (1) the ECL catalysis for Ru(bpy)32+was performed by electro-inducing the DpAg particles to generate Ag+ion and controlled by the special potential. The catalyzer Ag+was produced near the electrode surface and reproduced by cyclic potential scan, which improved the catalytic efficiency. (2) The amount of the ECL signal probes linked to secondary antibodies were amplified by the adsorption of Pt nanoparticles and the multiple sites bridge linkage of biotin/SA. These new multiple signal amplification strategies made the proposed ECL immunosensor achieve ultrasensitive detection for model protein human IgG with a detection limit down to 3 pg mL−1, which can be further extended to the detection of disease biomarkers. [ABSTRACT FROM AUTHOR]

highly sensitive amperometric immunosensor has been developed for the detection of carcinoembryonic antigen (CEA). It is based on (a) Prussian Blue nanoparticles coated with poly(diallyldimethylammonium chloride) (P-PB) and (b) double-layer gold nanocrystals. The sensor was obtained by first electrodepositing porous gold nanocrystals on the glassy carbon electrode (GCE), and then by modifying the electrode with the coated P-PB. Subsequently, colloidal gold nanoparticles (nano-Au) were adsorbed onto the GCE by electrostatic interactions between the negatively charged nano-Au and the positively charged P-PB to immobilize CEA antibodies. Finally, bovine serum albumin was employed to block possible remaining active sites and to prevent the non-specific adsorption on the nano-Au. This immunosensor was characterized by cyclic voltammetry and scanning electron microscopy. The working range was adjusted to two concentration ranges, viz. from 0.5 to 10 ng.mL, and from 10 to 120 ng.mL of CEA, with a detection limit of 0.2 ng.mL at three times the background noise. [ABSTRACT FROM AUTHOR]

The chitosan with three-dimensional porous structure greatly increased the effective electrode surface for loading of platinum nanoparticles and promoted efficient electron transfer. The resulting biosensor had a response time (within 5 s) and a linear response from 6 μM to 4.2 mM glucose with a detection limit of 2 μM (S/N = 3). Moreover, the methodology can be applied for the immobilization of other enzymes. [ABSTRACT FROM AUTHOR]

nonenzymatic sensor for hydrogen peroxide has been fabricated by dispersing platinum hollow nanospheres onto polypyrrole (PPy) nanowires to form a PPy-Pt hollow sphere nanocomposite on a glassy carbon electrode. The materials were characterized by transmission electron microscopy and scanning electron microscopy. The process and the sensor were characterized by electrochemical impedance spectroscopy, cyclic voltammetry, and chrono-amperometry and revealed that the electrode has a large electroactive surface area and small resistance to electron transfer. The linear range for the determination of hydrogen peroxide is from 3.5 µM to 9.9 mM, the detection limit is 1.2 µM (S/N = 3), and the response time is 3 s. The electrode exhibited good stability and excellent repeatability. [ABSTRACT FROM AUTHOR]

A novel amperometric immunosensor based on chitosan–gold nanoparticles (Chit–GNPs) composite film and thionine (Thi) was prepared for the determination of α-1-fetoprotein (AFP). The immunosensor was prepared by electro-depositing a Chit–GNPs composite matrix on the surface of the glass carbon electrode, then Thi was immobilized onto the Chit–GNPs film using glutaraldehyde as a cross-linker. Furthermore, the GNPs were chemisorbed onto Thi film for immobilization of α-1-fetoprotein antibody. The procedure of the immunosensor was characterized by means of cyclic voltammograms. The performance and influencing factors of the resulting immunosensor were studied in details. Under optimal conditions, the immunosensor was highly sensitive to AFP and the linear range covered from 0.40 to 200.0 ng mL−1 with a detection limit of 0.24 ng mL−1 at three times background noise. Moreover, the simple and controllable electro-deposition method overcame the irreproducibility for preparing Chit-based immunosensor systems and the proposed immunosensor displayed a satisfactory reproducibility and stability. [ABSTRACT FROM AUTHOR]

Abstract  [AuCl4]− was initially deposited by electrochemical reduction on a glassy carbon electrode (GCE) to form porous nanogold layer, then prussian blue (PB) was electrodeposited onto the as-prepared nanogold layer, and then secondary nanogold particles were fabricated again on the PB surface by electrochemical reduction for the immobilization of anti-CEA antibodies. The presence of double-layer porous gold nanoparticles enhanced the immobilized amount of biomolecules, and improved the sensitivity of the immunoassay. PB, as a good redox probe, was facile to electrochemical analysis and measurement. Under optimal conditions, the developed immunoassay exhibited dynamic range from 3.0 to 80.0 ng/mL with a detection limit of 0.9 ng/mL CEA (S/N = 3). Moreover, the selectivity, reproducibility and stability of the immunosensor were acceptable. [ABSTRACT FROM AUTHOR]

An immunosensor has been fabricated for direct amperometric determination of carcinoembryonic antigen. It is based on a biocompatible composite film composed of porous chitosan (pChit) and gold nanoparticles (GNPs). Firstly, a pChit film was formed on a glassy carbon electrode by means of electrodeposition. Then, thionine as a redox probe was immobilized on the pChit film modified electrode using glutaraldehyde as a cross-linker. Finally, GNPs were adsorbed on the electrode surface to assemble carcinoembryonic antibody (anti-CEA). The surface morphology of the pChit films was studied by means of a scanning electron microscope. The immunosensor was further characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical behaviors and factors influencing the performance of the resulting immunosensors were studied in detail. Results showed that the pChit films can enhance the surface coverage of antibodies and improve the sensitivity of the immunosensor. Under optimal conditions, the immunosensor was highly sensitive to CEA with a detection limit of 0.08 ng·mL−1 at three times the background noise and linear ranges of 0.2∼10.0 ng·mL−1 and 10.0∼160 ng·mL−1. Moreover, the immunosensor exhibited high selectivity, good reproducibility and stability. [ABSTRACT FROM AUTHOR]

A third-generation mediator-free hydrogen peroxide biosensor was fabricated by combining electrodeposition and self-assembly techniques. In this strategy, Au-Pt hybrid nanoparticles were electrodeposited on a film of polypyrrole, and L-cysteine was assembled to their surface by exploiting the strong affinity between mercapto groups and nanoparticles. Then, DNA and horseradish peroxidase were respectively self-assembled on the surface of the electrode. The resulting electrode was characterized by impedance spectroscopy, and the electrode surface (without enzyme) was characterized by scanning electron microscopy. The response of the sensor towards hydrogen peroxide, as investigated by cyclic voltammetry and chronoamperometry, is linear between 4.9 µM to 4.8 mM, with a detection limit of 1.3 µM (at an S/N of 3). The apparent Michaelis-Menten constant $$ \left( {K_M^{app}} \right) $$ is 0.69 mM. [ABSTRACT FROM AUTHOR]

Abstract  A novel amperometric hydrogen peroxide biosensor based on the immobilization of hemoglobin on the 2,6-pyridinedicarboxylic acid (PDC) polymer, thionine and nano-Au was successfully fabricated. In this strategy, PDC polymer acted as the matrices to covalently immobilize the thionine, and then hemoglobin was successfully adsorbed on the nano-Au which was electro-deposited on to thionine modified electrode surface. The preparation process of modified electrode was characterized with electrochemical impedance spectroscopy and atomic force microscope. The analytical performance of proposed biosensor toward H2O2 was investigated by cyclic voltammetry and chronoamperometry. The resulted biosensor exhibited fast amperometric response (within 6 s) to H2O2, and linear range was from 9.1 μM to 5.0 mM with the detection limit of 2.6 μM (S/N = 3). The apparent Michaelis–Menten constant (K Mapp) was evaluated to be 3.2 mM. Furthermore, the resulted biosensor showed good stability and reproducibility. [ABSTRACT FROM AUTHOR]

Abstract  A novel and convenient immunosensor, based on the electrostatic adsorption characteristics between the positively charged MnO2 nanoparticles (nano-MnO2) and chitosan (CS) composite membrane (nano-MnO2 + CS) and the negatively charged prussian blue (PB), was prepared for the detection of carcinoembryonic antigen (CEA). Firstly, PB was electro-deposited on the surface of the gold electrode in the constant potential, and then nano-MnO2 + CS was adsorbed onto PB-modified electrode surface. Subsequently, Gold nanoparticles (nano-Au) were electro-deposited on the nano-MnO2 + CS-modified electrode to immobilize antibody CEA (anti-CEA). Finally, bovine serum albumin (BSA) was employed to block sites against nonspecific binding. In our study, cyclic voltammetry (CV) and scanning electron microscopy (SEM) were used to characterize the fabricated process of the immunosensor. The immunosensor put up a rapid response time, high sensitivity and stability. Under the optimized conditions, cyclic voltammograms(CVs) determination of CEA displayed a broader linear response to CEA in two ranges, from 0.25 to 8.0 ng/mL, and from 8.0 to 100 ng/mL, with a relative low-detection limit of 0.083 ng/mL at three times the background and noise. The originality of the preparation of the immunosensor lies in not only using the synergistic effect of two kinds of nanomaterials (nano-MnO2 and nano-Au) to immobilize anti-CEA, but also using nano-MnO2 + CS to furnish a media transferring electron path. What is more, the researched methodology was efficient and potentially attractive for clinical immunoassays. [ABSTRACT FROM AUTHOR]

An amperometric carcinoembryonic antigen (CEA) immunosensor was fabricated based on Prussian blue (PB), nano-calcium carbonate (nano-CaCO3) and nano-gold modified glassy carbon electrode. First, PB as a mediator was deposited on glassy carbon electrode to obtain a negatively charged surface. Then, positive nano-CaCO3 was adsorbed on the PB modified electrode through electrostatic interaction. Subsequently, gold nanoparticles were deposited on the nano-CaCO3/PB modified electrode. The use of two kinds of nanomaterials (nano-CaCO3 and nano-gold) with good biocompatibility as immobilization matrixes not only provides a biocompatible surface for protein loading but also avoids the leaking of PB. The size of nano-CaCO3 was characterized by transmission electron microscopy (TEM). The factors influencing the performance of the immunosensor presented were studied in detail. Under the optimized conditions, cyclic voltammograms (CV) determination of CEA showed a specific response in two concentration ranges from 0.3 to 20 ng mL−1 and from 20 to 100 ng mL−1 with a detection limit of 0.1 ng mL−1 at a signal-to-noise ratio of 3. The immunosensor presented exhibited high selectivity, sensitivity and good stability. [ABSTRACT FROM AUTHOR]

Abstract  A novel amperometric immunosensor for human chorionic gonadotropin (HCG) assay has been fabricated through incorporating toluidine blue (TB) and hemoglobin (Hb) on the multiwall carbon nanotube (MWNT)–chitosan (CS) modified glassy carbon electrode, followed by electrostatic adsorption of a conducting gold nanoparticles (nanogold) film as sensing interface. The MWNT–CS matrix provided a congenial microenvironment for the immobilization of biomolecules and promoted the electron transfer to enhance the sensitivity of the immunosensor. Due to the strong electrocatalytic properties of Hb and MWNT toward H2O2, the Hb and MWNT significantly amplified the current signal of the antigen–antibody reaction. The immobilized toluidine blue as an electron transfer mediator exhibited excellent electrochemical redox property. After the immunosensor was incubated with HCG solution, the access of activity center of the Hb to toluidine blue was partly inhibited, which leaded to a linear decrease in the catalytic efficiency of the Hb to the oxidation of immobilized toluidine blue by H2O2 over HCG concentration ranges from 0.8 to 500 mIU/mL. Under optimal condition, the detection limit for the HCG immunoassay was 0.3 mIU/mL estimated at a signal-to-noise ratio of 3. Moreover, the proposed immunosensor displayed a satisfactory stability and reproducibility. [ABSTRACT FROM AUTHOR]

Gold nanowires with of designed length on a solid substrate have been proven as an efficiently immobilized affinity support for the detection of carcinoma antigen 125 (CA 125) in this study. The presence of gold nanowires provides a well-defined three-dimensional structure, and greatly amplifies the coverage of the anti-CA 125 protein on the probe surface. Moreover, the amount of anti-CA 125 varied with the change of the morphology of the probe, and achieved an optimal quartz crystal microbalance (QCM) response towards anti-CA 125 adsorption at the number of gold nanolayers of 5. The formed immune-probe exhibits good QCM responses for the detection of CA 125, and allows the detection of CA 125 at concentrations as low as 0.5 U ml−1. The QCM immunosensor exhibited good precision, high sensitivity, acceptable stability, accuracy and reproducibility. The as-prepared immunosensors were used to analyze CA 125 in human serum specimens. Analytical results suggest that the developed immunoassay method is a promising alternative approach for detecting CA 125 in the clinical diagnosis. Compared with conventional ELISA, the proposed immunoassay system was simple and rapid without multiple labeling and separation steps. Importantly, the route provides an alternative approach to incorporate multiple gold nanolayers onto the solid matrix for biosensing applications. [ABSTRACT FROM AUTHOR]

In this paper, a H202 biosensor was propose~1. At first, an organic conductive material, 3,4,9,1 0-perylenetetracarboxylic acid- toluidine blue (P1'ATB), was synthesized by 3,4,9,10-perylenetetracarboxylic dianhydride and toluidine blue. Then the prepared PTATB was dispersed into Ti02 solution and dropped on a glassy carbon electrode to form a stable Ti02-PTATB composite film with efficient redox activity. Later, gold nanoparticles (GNPs) were carbonylated by O-carboxymethyl chitosan (CMCS) to obtain functionalized gold nanoparticles (CMCS-GNPs), which were adsorbed on the Ti02-PTATB film with positive charge via elec- trostatic interaction. Finally, hemoglobin, as a model enzyme, was covalently immobilized onto the electrode modified with CMCS-GNPs/Ti02-PTATB matrix to construct a new H202 biosensor. The proposed biosensor displays a high sensitivity, fast analytical time, and broader linear response to H202 in the range from 1.4 X lO6 to 1.6 X lO~ M with a limit of detection of 3.7 X lO~ M at 3 times the background noise. The apparent Michaelis-Menten constant (Ky) and the maximum current density (1'max) for the proposed biosensor were estimated to be 0.62 mM and 211 p~A/cm2, respectively. This work provided a new avenue for the electrochemical investigation of enzyme immobilization. [ABSTRACT FROM AUTHOR]

Abstract  A new protein assay system for the antigen–antibody interaction was developed by immobilization of carcinoembryonic antibody (anti-CEA) onto magnetic-core/gold-shell nanoparticles-functionalized biomimetic interface on multiporous polythionine modified magnetic carbon paste electrodes (MCPE). Differential pulse voltammetric (DPV) technique was employed to investigate the antigen–antibody interaction in pH 6.8 acetate acid buffer solution after incubation with various CEA samples for 50 min at room temperature. The peak currents decreased with increased CEA concentration, and were proportional to the CEA concentration in the range of 1.5–60 ng/ml with a detection limit of 0.3 ng/ml at a signal-to-noise ratio of 3. Moreover, the selectivity, reproducibility and stability of the proposed immunoassay system were acceptable. Compared with the conventional immunoassays, the developed immunoassay system was simple and rapid without multiple labeling and separation steps. Importantly, the proposed methodology would be valuable for diagnosis and monitoring of carcinoma and its metastasis. [ABSTRACT FROM AUTHOR]

Abstract  A new strategy for immobilization of horseradish peroxidase (HRP) has been developed by self-assembling gold nanoparticles to multiporous polythionine (PTH) film modified carbon paste interface. A thionine film was initially electropolymerized onto carbon paste interface in a mildly acidic thionine solution at a bias voltage of −1.0 to 1.5 V. This process is accompanied by the hydrogen evolution reaction, and the released hydrogen gas made the PTH film with multiporous structure. The multiporous PTH film provided a biocompatible microenvironment for gold nanoparticles and enzyme molecules, and greatly amplified the coverage of HRP molecules on the electrode surface. Voltammetric and time-based amperometric techniques were employed to characterize the properties of the derived biosensor. The performance and factors influencing the performance of the biosensor were also proposed. The immobilized HRP displayed a catalytic property to the reduction of H2O2. The H2O2biosensor achieved 95% of the steady-state current within 2 s, and exhibited a linear range of 9.6?10−6to 1.2?10−3 M H2O2with a detection limit of 7.5?10−7 M (S/N= 3). Furthermore, the biosensor remained at about 90% of its original sensitivity after 2 weeks’ storage. [ABSTRACT FROM AUTHOR]

A novel H2O2 biosensor is described which is based on immobilization of horseradish peroxidase (HRP) on DNA/electrodeposited, ZrO2/modified, gold electrode. The DNA is attached via its 5′ end to ZrO2 and this provides a microenvironment for the immobilization of various biomolecules and promotes electron transfer between HRP and the electrode surface. Under optimized conditions, the biosensor reduced H2O2 linearly between 3.5 μM and 10 mM with a detection limit of 0.8 μM at a signal-to-noise ratio of 3. In addition, the developed biosensor shows an acceptable stability and repeatability. Importantly, the analytical methodology could be further developed for the immobilization of other proteins and biocompounds. [ABSTRACT FROM AUTHOR]

Abstract??A mediator-free amperometric hydrogen peroxide biosensor was prepared by immobilizing horseradish peroxidase (HRP) enzyme on colloidal Au modified platinum (Pt) wire electrode, which was modified by poly 2,6-pyridinediamine (pPA). The modified process was characterized by electrochemical impedance spectroscopy (EIS), and the electrochemical characteristics of the biosensor were studied by cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The biosensor displayed an excellent electrocatalytical response to reduction of H2O2without the aid of an electron mediator, the linear range was 4.2???10?7?1.5???10?3?mol/L (r?=?0.9977), with a detection limit of 1.4???10?7?mol/L. Moreover, the performance and factors influencing the resulted biosensor were studied in detail. The studied biosensor exhibited permselectivity, good stability and good fabrication reproducibility. [ABSTRACT FROM AUTHOR]

A new electrochemical biosensor for determination of hydrogen peroxide (H2O2) has been developed by immobilizing horseradish peroxidase (HRP) on silver colloids (nanosilver) and use of a DNA-functionalized interface. In the presence of the DNA and the nanosilver the immobilized HRP gives a pair of well-defined redox peaks with an electron-transfer rate constant of 3.27 ± 0.91 s−1 in pH 7.0 PBS. The presence of DNA also provides a biocompatible microenvironment for enzyme molecules, greatly amplifies the amount of HRP molecules immobilized on the electrode surface, and improves the sensitivity of the biosensor. Under optimum conditions the biosensor has electrocatalytic activity in the reduction of hydrogen peroxide with linear dependence on H2O2 concentration in the range 1.5 × 10−6 to 2.0 × 10−3 mol L−1; the detection limit is 5.0 × 10−7 mol L−1 at a signal-to-noise ratio of 3. The $$ K^{{{\text{app}}}}_{{\text{m}}} $$ value of HRP in the composite membrane was found to be 1.62 mmol L−1. These results suggest that the properties of the complex film, with its bioelectrochemical catalytic activity, could make it useful for development of bioelectronic devices and for investigation of protein electrochemistry at functional interfaces. [ABSTRACT FROM AUTHOR]

A direct electrochemical immunoassay system based on the immobilization of α-1-fetoprotein antibody (anti-AFP), as a model system, on the surface of core-shell Fe2O3/Au magnetic nanoparticles (MNP) has been demonstrated. To fabricate such an assay system, anti-AFP was initially covalently immobilized on to the surface of core-shell Fe2O3/Au MNP. Anti-AFP-modified MNP (bio-nanoparticles) were then attached to the surface of carbon paste electrode with the aid of a permanent magnet. The performance and factors influencing the performance of the resulting immunosensor were studied. α-1-Fetoprotein antigen was directly determined by the change in current or potential before and after the antigen–antibody reaction versus saturated calomel electrode. The electrochemical immunoassay system reached 95% of steady-state potential within 2 min and had a sensitivity of 25.8 mV. The linear range for AFP determination was from 1 to 80 ng AFP ml−1 with a detection limit of 0.5 ng AFP ml−1. Moreover, the direct electrochemical immunoassay system, based on a functional MNP, can be developed further for DNA sensor and enzyme biosensor. [ABSTRACT FROM AUTHOR]

A novel method for fabrication of a diphtheria potentiometric immunosensor has been developed by means of self-assembling compound nanoparticles to a thiol-containing sol-gel network. A cleaned gold electrode was first immersed in a 3-mercaptopropyltrimethoxysilane (MPS) sol-gel solution to assemble a silica sol-gel monolayer. The silane entities were then polymerized into a two-dimensional sol-gel network (2D network) by dipping into aqueous NaOH. The second silane layer was formed by re-immersion in the MPS sol-gel solution overnight. The compound nanoparticles (nanocompounds) containing gold nanoparticles and silver nanoparticles were then chemisorbed on to the thiol groups of the second silane layer. Finally, diphtheria antibody (anti-Diph) was adsorbed on to the surface of the compound nanoparticles. The modified process was characterized by cyclic voltammetry (CV). Detection is based on the change in the potentiometric response before and after the antigen-antibody reaction. A direct potentiometric response to diphtheria antigen (Diph) was obtained from the immobilized diphtheria antibody. The potentiometric response of the resulting immunosensor was rapid and the linear range was from 22 to 800 ng mL-1 with the linear regression equation ?E=-79.5+69.4 log [Diph] and a detection limit of 3.7 ng mL-1 (at 3d). Up to 19 successive assay cycles with retention of sensitivity were achieved for probes regenerated with 0.2 mol L-1 glycine-hydrochloric acid (Gly-HCl) buffer solution. Moreover, analytical results from several serum samples obtained using the developed technique were in satisfactory agreement with those given by the ELISA method, implying a promising alternative approach for detecting diphtheria antigen in clinical diagnosis. [ABSTRACT FROM AUTHOR]

A bifunctional probe (PTC-Tb) which acts as not only a well-defined and stable electrochemical redox molecule but also as a highly efficient co-reactant of an electrochemiluminescent oxygen-peroxydisulfate system was firstly synthesized and applied to the construction of dual-response aptasensors for thrombin detection. [ABSTRACT FROM AUTHOR]

The association of the target thrombin with the corresponding aptamer leads to structure switching of the dsDNA probes and the formation of nicking sites for exonuclease III, which causes cyclic cleavage of the dsDNA probes and highly reduced intercalation of the electrochemiluminescent signal indicators for labelfree and sensitive detection of thrombin at the femtomolar level. [ABSTRACT FROM AUTHOR]

A highly sensitive electrochemical aptasensor for thrombin detection is developed and demonstrated by using porous platinum nanotubes modified with polyamidoamine dendrimers as nanocarriers and electrocatalysts. The proposed strategy affords a low detection limit of 0.03 pM based on enzyme-based signal amplification. [ABSTRACT FROM AUTHOR]

The presence of exonuclease III leads to direct recycling and reuse of the target DNA, which in turn results in substantial signal amplification for highly sensitive, label-free impedimetric detection of specific DNA sequences. [ABSTRACT FROM AUTHOR]

Optical properties of a concentric silver-atomic medium nanoshell are investigated based on the quasi-static and Maxwell-Garnett approximations. We consider the atomic medium as K-type three-level atoms driven simultaneously by a coupling field and a probe field. It is shown that the strong coupling between atoms and sphere plasmon of silver core emerges of multiple-mode and ultra narrow-band absorption spectra by controlling the permittivity of the atomic medium. In particular, coherent driving of the coupling field allows us to manipulate surface plasmon resonances, including frequency shift and bandwidth modification. Furthermore, we demonstrate that selective absorption enhancement of different modes can be achieved by tuning the radius of the core and the shell. These absorption properties yield potential applications of the nanoshells as ultracompact tunable nonlinear optical devices. [ABSTRACT FROM AUTHOR]

A new signal amplification strategy based on thionine (TH)-doped magnetic gold nanospheres as labels and horseradish peroxidase (HRP) as enhancer holds promise to improve the sensitivity and detection limit of the immunoassay for carcinoembryonic antigen (CEA), as a model protein. This immunoassay system was fabricated on a carbon fiber microelectrode (CFME) covered with a well-ordered anti-CEA/protein A/nanogold architecture. The reverse micelle method was initially used for the preparation of TH-doped magnetic gold nanospheres (nanospheres), and the synthesized nanospheres were then labeled on HRP-bound anti-CEA as a secondary antibody (bionanospheres). Sandwich-type protocol was successfully introduced to develop a new high-efficiency electrochemical immunoassay with the labeled bionanospheres toward the reduction of H2O2. Under optimized conditions, the linear range of the proposed immunoassay without HRP as enhancer was 1.2-125 ng/mL CM, whereas the assay sensitivity by using HRP as enhancer could be further increased to 0.01 ng/mL with the linear range from 0.01 to 160 ng/mL CM. The developed immunoassay method showed good precision, high sensitivity, acceptable stability and reproducibility, and could be used for the detection of real samples with consistent results in comparison with those obtained by the enzyme-linked immunosorbent assay (ELISA) method. [ABSTRACT FROM AUTHOR]

In this work, based on terminal protection of folate-linked ssDNA (FA-ssDNA) and the SYBR Gold fluorescent dye, we describe the development of a label-free fluorescent strategy for the detection of folate receptors (FRs). The binding between the target FR and the FA moiety of the FA-ssDNA protects the FR bound FA-ssDNA from digesting by Exo I. The binding of SYBR Gold to the terminal protected, un-digested FA-ssDNA leads to enhanced fluorescent emission for the monitoring of FR with a detection limit of 30 pM. Besides, the developed method also shows high selectivity toward FR against other control proteins. Moreover, our approach avoids the labeling of the probes with fluorescent tags and achieves label-free detection of FR. With these advantages, the proposed method thus holds promising potential for the development of simple and convenient strategies for the detection of other proteins by using different small molecule receptor/protein ligand pairs. [ABSTRACT FROM AUTHOR]

A procedure for fabricating an enzyme electrode has been described based on the effective immobilization of horseradish peroxidase (HRP) to a nano-scaled particulate silver (nano-Ag)-modified platinum electrode with polyvinyl butyral (PVB) as the matrix. The hydrogen peroxide concentration was determined in the presence of azure C as a mediator to transfer electrons between the electrode and HRP. The HRP immobilized on colloidal Ag was stable and retained its biological activity. The biosen-sor displayed excellent electrocatalytic activity to the reduction of H2O2 . The characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The effects of experimental variables such as the operating potential of the working electrode, mediator concentration, pH and temperature of the measuring solution were investigated for optimum analytical performance by using an amperometric method. Linear calibration for H2O2 was obtained in the range 2.0 x10-6 to 6.0 x 10-3 M under the optimized conditions. The sensor was highly sensitive to H2O2 with a detection limit of 1.0 x 10-6 Mand the sensor achieved 95% of the steady-state current within 5 s. The sensor exhibited high sensitivity and stability. [ABSTRACT FROM AUTHOR]